The present invention relates to a method for producing a fibrous fire protection agent composed of fibrous materials having boric acid particles adhering to their surfaces, and possibly other adhering materials, particularly glass and ceramic forming minerals.
Fire protection agents are available almost exclusively in the form of bromine, boron, or salts such as bromates, borates, phosphates, sulfates and the like. These salts are mixed, possibly with one another or with other additives, and are sold in ground or powdered form.
Such agents are all water soluble to a greater or lesser degree; therefore, the products to be protected are generally saturated with an aqueous solution of these salts. However, for many of the products to be protected, saturation is impossible; in such cases, the fire protection agents must then be mixed with or dispersed in powdered form among the raw materials serving to produce these products. Such admixture is successful, or results in homogeneous mixtures in which the fire protection agent is uniformly distributed throughout the entire volume of the product, only if such fire protection agents are mixed with other powdered substances.
If the starting raw materials are coarse-grained or of large-area or are raw materials having substantially different weights per unit volume than the fire protection agents, manufacture, and particularly the retention of a homogeneous mixture, becomes impossible since in the course of processing, the fire protection agents will separate again from the raw materials. For example, it is impossible to mix powdered boric acid with wood chips in order to produce fire protected chip boards since the boric acid particles separate from the wood chips already during spreading of the chip cake and collect at the bottom of the chip cake.
It has therefore been proposed to saturate such raw materials with the above-mentioned fire protection agent solution; but this is unacceptable not only for economic reasons but also because the raw materials are impossible to use if the saturation prevents bonding of the individual raw material particles to one another. This is again the case, for example, in the manufacture of wood chip boards where such a saturation impedes the gluing together of the individual wood chips in such a manner that the finished product no longer has the desired strength.
In order to overcome these difficulties, it has been proposed to utilize fire protective fibers, that is fibers which have adsorbed the fire protection agents. Such fibers do not demix from the coarse-grained or large-area raw materials even under heavy vibrations so that products made from these raw materials are provided with fire protection agents throughout their entire volume.
Various methods have been developed for bonding the fire protection agents to the fibers. A very economical and dependable method is grinding the powdered fire protection agents together with granulates containing fibers in an impact pulverizer, during which process the fire protection agents adhere to the fibers due to molecular attraction forces. A further prior art process using boric acid as the fire protection agent is carried out by mixing boron minerals with finely comminuted carrier substances, which may also be present in fibrous form, and then spraying the mixture with a mineral acid in such concentration and quantity that the boron minerals are converted to boric acid. During this process, the boric acid particles adhere to the finely dispersed carrier substances, again forming, if fibrous carrier substances are used, fire protective fibers.
The present invention relates more specifically to further developments of the last-mentioned process, using fibers as carrier substances but causing not only boric acid particles to adhere to the fibers but also further materials serving to provide fire protection for or an improvement of the materials for the products produced therefrom. Use is particularly made of glass and ceramic forming materials, which, in the case of fire, contribute greatly to increased fire protection by encapsulating the raw materials.
The manufacture of such fire protective fibers has previously been effected by mixing the dry fiber substances with the powdered boron minerals and then, in continuation of the mixing process, spraying in mineral acid in appropriate concentration and quantity. The prerequisite for the practice of this method is, firstly, the presence of dry fiber substances and powdered boron minerals and, secondly the presence of mineral acid in the appropriate concentration and quantity.
In order to economically produce such fire protective fibers it has also been proposed to use fibers which are carried along in residual waste water clarification sludges, particularly those originating from paper, cardboard and cellulose manufacture. The drawback of the use of these fibers is that these residual waste water clarification sludges must first be processed, particularly before being employed in the prior art method, and must be dried. It would also be advisable, for economic manufacture of the fire protective fibers, if concentrated sulfuric acid, which appears in large quantities as a byproduct in various industrial processes, could be used in the practice of the prior art method. However, with such cellulose fibers this is impossible since these fibers would be destroyed by the concentrated sulfuric acid. The sulfuric acid must therefore be diluted to a concentration of less than 50% by weight. Drying of the residual waste water clarification sludges as well as the required dilution of the sulfuric acid make the prior art method so much more expensive that fire protective fibers are used only with reluctance in spite of their eminent advantages.
A fire protective fiber material produced according to the prior art method contains, aside from the fiber, about 40-45 percent by weight boric acid, about 50-55 percent by weight calcium sulfate, with any remainder being water. In case of fire, the fire protective effect of these protective fibers is thus created exclusively by the action of the boric acid. Glass and ceramic forming minerals cannot be found in such a fire protective fiber.